Created attachment 8903251 [details] black scrollbars I just noticed this in the 2017-08-30 nightly on Windows 10 on a Surface Book. Moving the cursor over where the scrollbars are doesn't make them paint.
This happens with horizontal scrollbars, too, in case is matters.
Andrew, are you still able to reproduce this issue? Do you see the black scroll on the other content process? What happens if you load a new page?
I haven't seen it this week but when I did it was in all content processes and in all tabs (existing and new ones).
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